Cation induced conformation changes in hyaluronate solution

The influence of barium as a bivalent metal cation on the molecular conformation of partially deprotonated hyaluronic acid is studied by viscosimetry and atomic force microscopy (AFM). The resulting data are compared with corresponding observations on dextran as an uncharged representative of the group of polysaccharides. Titrations monitored by rotational viscosimetry and conductometry are carried out using diluted aqueous solutions of hyaluronate and dextran, stepwise adding small amounts of a Ba2+ solution. The AFM measurements are performed on single molecules of hyaluronate and dextran in absence and presence of Ba2+ ions. The cation induced conformational changes lead to a decrease of the solution viscosity in case of the hyaluronate. The corresponding AFM micrographs reveal that Ba2+ ions induce a transformation from extended and slightly curved chains to internally linked molecules exhibiting sharp bends and significantly smaller hydrodynamic radii. In contrast, the solution viscosity and the conformation of dextran remain largely unchanged in presence of barium.